1. Field of the Invention
The present invention relates to a chemical reaction apparatus and a power supply system including this chemical reaction apparatus and, more particularly, to a chemical reaction apparatus applied to a power supply system including a fuel cell which generates electric power by using fuel.
2. Description of the Related Art
Conventionally, chemical reaction apparatuses are known in the field of chemical reaction engineering. In these chemical reaction apparatuses, various fluidized material mixtures are supplied to a reaction flow path, and a desired fluid material is produced by a chemical reaction caused by a catalyst formed in the reaction flow path, i.e., by a catalyst reaction.
These chemical reaction apparatuses have various sizes and structures in accordance with their applications. Recently, in this technical field of chemical reaction apparatuses, some chemical reaction apparatuses have been developed in which a millimeter-order or micron-order flow path is formed in a microspace of a silicon chip by using a so-called micromachine fabrication technology represented by the micropatterning technology developed in the technology of fabricating semiconductor devices such as integrated circuits, and a fluid material is supplied to the flow path to cause a predetermined chemical reaction.
FIG. 13A is an opened-up sectional view taken along a Y—Y line of an example of the conventional chemical reaction apparatuses of this sort. FIG. 13B is an opened-up sectional view taken along an X—X line of the apparatus. FIG. 13C is an opened-up sectional view taken along a Z—Z line of the apparatus. To clarify the arrangement of this chemical reaction apparatus, the shape of a reaction flow path and the planar shape of a thin-film heater are hatched for the sake of convenience.
FIGS. 14A to 14C are schematic views for explaining the steps of the fabrication process of the chemical reaction apparatus.
As shown in FIGS. 13A and 13B, a chemical reaction apparatus 60p has a reaction flow path 20p formed as a trench having a micron order width and depth in one surface of a main substrate 10p which is a silicon substrate or the like by using, e.g., photoetching. For example, a predetermined catalyst 25p is adhered to the inner wall surfaces of the reaction flow path 20p. In side portions of the main substrate 10p, a supply port 20a and discharge port 20b for supplying and discharging a fluid material to and from the reaction flow path 20p are formed. A closing substrate 30p such as a glass plate is bonded to said one surface of the main substrate 10p to close the open end of the trench of the reaction flow path 20p. 
As shown in FIGS. 13B and 13C, a thin-film heater 40p is provided on the other surface of the closing substrate 30p. The thin-film heater 40p is a heating resistor or the like and has a shape identical or close to the shape of the reaction flow path 20p. The thin-film heater 40p generates heat and heats the interior of the reaction flow path 20p, thereby supplying thermal energy required for a chemical reaction to the reaction flow path 20p. 
Recently, research and development for downsizing power supply systems using fuel cells have been extensively done. A chemical reaction apparatus having the above arrangement can be applied to those power supply systems using fuel cells. That is, power generation fuel is supplied to the chemical reaction apparatus as described above to produce hydrogen gas by a predetermined chemical reaction. Electric power can be generated by supplying this hydrogen gas to a fuel cell.
This chemical reaction apparatus has the following various characteristic features resulting from micropatterning of the reaction flow path. That is, since the reaction flow path is micropatterned, the reaction volume of this reaction flow path decreases. Since this increases the ratio of the surface area between the reaction flow path and heater to the volume of the reaction flow path, the heat conduction characteristics upon a catalyst reaction improve, and this increases the reaction efficiency of the chemical reaction. The decreased sectional area of the reaction flow path shortens the diffusion/mixing time of reaction molecules of a fluid material supplied to the reaction flow path. This increases the rate of progress of the chemical reaction in the reaction flow path. Furthermore, the arrangement of the chemical reaction apparatus itself is downsized. This eliminates complicated reaction engineering examination, such as applied when a large-sized furnace is to be manufactured, resulting from stepwise scale-up matching the results of examination using a small-sized experimental furnace.
Unfortunately, the above chemical reaction apparatus has the following problems.
In the fabrication process of the chemical reaction apparatus 60p described above, as shown in FIG. 14A, a reaction flow path 20p is first formed as a trench having a predetermined sectional shape and flow path shape in one surface of a substrate material serving as the main substrate 10p. 
As shown in FIG. 14B, a thin-film heater 40p having a planar shape identical or close to the flow path shape of the trench is provided on one surface of a substrate material serving as the closing substrate 30p. 
Then, as shown in FIG. 14C, the main substrate 10p and closing substrate 30p are aligned such that the position of the reaction flow path 20p which is the trench formed in the main substrate 10p and the position of the thin-film heater 40p formed on the closing substrate 30p accurately correspond to each other, and said one surface of the main substrate 10p and the other surface of the closing substrate 30p are bonded.
When the trench of the reaction flow path 20p and the corresponding thin-film heater 40p are formed by micron-order dimensions as described above, fine positional shift during alignment of the main substrate 10p and closing substrate 30p leads to positional shift between the reaction flow path 20p and thin-film heater 40p. This positional shift has large influence on, e.g., the reaction characteristics of the chemical reaction. Therefore, the accuracy of alignment of the two substrates must be very high. This may make the operation in the substrate bonding step complicated and time-consuming, or may require a high-accuracy fabrication apparatus to increase the cost.
Also, in the structure in which the open end of the trench of the reaction flow path 20p is closed by bonding the main substrate 10p and closing substrate 30p as described above, if bonding or adhesion between the two substrates is unsatisfactory, a fluid material flowing in the reaction flow path 20p may leak, or the two substrates may peel off or break owing to a thermal expansion coefficient difference between them. This sometimes poses reliability problems such as deterioration of the reaction characteristics of the chemical reaction apparatus, defective operations, and contamination to peripheral devices.
In the above chemical reaction apparatus, a Ta—Si—O-based compound is sometimes used as a heating resistor material forming the thin-film heater because the compound has appropriate resistivity. To improve the heat conduction characteristics of thermal energy from the thin-film heater to the reaction flow path and increase the reaction efficiency of the chemical reaction, the thin-film heater can be exposed to the reaction flow path. In this case, according to inspection by the present inventors, if the compound as described above is used as the heating resistor material, a fluid material produced by the chemical reaction, particularly, hydrogen gas may enter the material forming the thin-film heater to deteriorate the film quality, thereby deteriorating the heating characteristics of the thin-film heater and lowering the reaction efficiency.
FIG. 15 is a view showing the main parts of an arrangement pertaining to temperature control in a heat-treatment apparatus using the chemical reaction apparatus 60p described above.
In this heat-treatment apparatus, the temperature of the reaction flow path 20p of the chemical reaction apparatus must be accurately controlled to efficiently perform the chemical reaction. Therefore, as shown in FIG. 15, this conventional apparatus has a temperature sensor 101 installed near the reaction flow path 20p in order to perform temperature control. The temperature sensor 101 is connected to a temperature measuring unit 103 via a line 102, and the temperature measuring unit 103 measures the internal temperature of the reaction flow path 20p. The thin-film heater 40p of the chemical reaction apparatus 60p is connected to a power supply unit 105 via a line 104. On the basis of the temperature measured by the temperature measuring unit 103, a temperature controller 106 controls electric power supplied from the power supply unit 105 to the thin-film heater 40p, thereby holding the internal temperature of the reaction flow path 20p at a temperature appropriate for a desired chemical reaction. One end portion of the reaction flow path 20p is connected to the end of a supply pipe 21a, and the other end portion of the reaction flow path 20p is connected to the end of a discharge pipe 21b. 
Thermal energy generated by the thin-film heater 40p is desirably used in the chemical reaction. However, the line 102 is a low-resistance conductor and at least partially contains a metal. Since the metal has high thermal conductivity, a port of the thermal energy supplied into the reaction flow path 20p through the line 102 is conducted outside the chemical reaction apparatus 60p, thereby producing thermal energy loss. When the chemical reaction apparatus 60p is large, this thermal energy loss is negligibly small. However, as downsizing of this chemical reaction apparatus advances, the ratio of the thermal energy loss increases, and this decreases the energy utilization.